1. Technical Field
The present invention relates to a new and improved apparatus and method for sharpening tool bits, particularly a carbide router or shaper bit.
2. Brief Description of the Prior Art
Routers and shapers have become two of the most important tools in a Woodworker's shop. A router and shaper bit sharpening device must meet three criteria to be desirable to professional and non-professional sharpeners. It must be inexpensive, easy to use, and effective. No conventional sharpener has achieved these goals. Professional grinding equipment can cost up to five hundred thousand dollars. Inexpensive devices are difficult to use and ineffective.
Router and shaper bits have multiple blades attached to the shaft of the bit at roughly right angles to the shaft. To use any router bit sharpening device, each blade has to be sharpened individually. To sharpen each blade, the face of the blade must first be made parallel to the face of a grinding wheel. With conventional sharpeners, this is achieved by coloring the face of the blade, attempting to align the blade by eye, and then swiping the blade with the grinding wheel to check if it is parallel. Inevitably it must be readjusted several times and even then it is never quite right. With small router or shaper bits, this alignment is all but impossible. The small bits have so little surface area on the face of the blade that it is difficult to make the blade parallel to the face of a grinding wheel.
In addition, the hook and rake angle of each blade with respect to the bit shaft are usually different, due to the way the bits are made. Because of the difficulty of aligning a blade to the face of the grinding wheel, the person doing the sharpening makes only the first adjustment relying on that for all of the blades. This means that generally only the first blade is parallel to the grinding wheel. Subsequent blades end up wedge shaped when sharpened. As a result one blade is higher that the rest and does all of the cutting. The cut is not as clean and the bit becomes dull very quickly. Further, the sharpener may remove more material from each blade than is necessary in the effort to sharpen all of the blades, making future sharpening impossible.
Existing router bit sharpeners are designed to bring the bit into contact with the face of a grinding wheel by sliding the bit holder, during sharpening, in a direction perpendicular to the grinding wheel shaft. Any minute play in the sharpening machine or the grinding wheel results in a rounding over of the front edge of the router bit blade. While very high quality sharpeners have minimal play, the rounding over of the front edge of the bit is still a problem, particularly when disengaging the bit from a grinding wheel. The rounding over is much more acute with less expensive machines.
The prior art is illustrated in prior U.S. Pat. No. 5,816,898. The device of the patent is used with a grinding wheel mounted in a drill press. Referring in particular to FIG. 4 of the patent, a sharpening device is shown comprising a head 18 mounted on a head support 62. The head 18 supports a chuck 16 into which a bit is inserted. The bit is rotated in the chuck until the leading edge of the bit is generally parallel to the drill press table, and the bit is tightened in the chuck. This is a coarse adjustment for the hook angle of the bit. The adjusting screw 72 is then turned to adjust the shear angle of the bit bringing the face of the bit into a plane generally parallel to the face of the grinding wheel. The drill press is lowered until the drill press is directly over the bit to determine how parallel the face of the bit is to the grinding wheel. This adjustment process is repeated if necessary. The grinding wheel is turned on. The bit is brought in until the cutting face touches the wheel. The bit is then slid back and forth with the cutting face under the grinding wheel in a motion perpendicular to the grinding wheel shaft until sharpening is completed.
Any play in the system, inconsistencies in the table top, in the wheel, the drill press, or any other component of the apparatus, is translated to the critical point of contact between the bit cutting face and the edge of the grinding wheel resulting in rounding of the front edge of the bit.
It is an object of the present invention to provide a bit sharpening apparatus that is easier to use and achieves better quality sharpening.
It is further an object of the present invention to provide a bit sharpening apparatus or machine that minimizes the effects of play or inconsistencies in the machine. This decreases the tolerances to which the machine needs to be built allowing manufacture of the machine at a more reasonable cost affordable to small woodworkers and nonprofessional sharpeners.